The proposed research involves the use of a series of monoclonal antibodies that have been prepared against cell surface molecules of the rat central nervous system. These antibodies will be used to delineate a set of developmental parameters that will then allow a molecular analysis of development. The molecular nature of the antigens will be characterized by standard biochemical techniques. For those antigens found to be membrane proteins, the times of gene activation will be determined by in vitro translation of mRNA. Antigen expression by neural cells in tissue culture will be monitored by immunological techniques. Cell interactions and/or environmental factors influencing antigen expression will be determined. The sources and molecular nature of such developmental stimuli will be characterized. To study the mechanisms by which these stimuli influence specific gene activity, the DNA sequences coding for selected antigens will be studied using recombinant DNA technology. Cloned DNA sequences including putative promoter regions will be used in in vitro transcription assays to study the ways in which the identified developmental stimuli, or their derivatives, act at the level of the gene.